1. Technical Field of the Invention
The subject-matter of the invention is a cosmetic composition comprising, in a cosmetically acceptable medium, at least phloroglucinol or one of its derivatives.
Another subject-matter of the invention is the use of phloroglucinol or its derivatives in a cosmetic composition intended to promote epidermal renewal.
2. Description of Prior Art
The skin constitutes a physical barrier between the body and its environment. It is composed of two tissues, the epidermis and the dermis.
The dermis provides the epidermis with a solid backing. It is also its nutrient component. It is mainly composed of fibroblasts and of an extracellular matrix itself composed mainly of collagen, elastin and a so-called fundamental substance, these components being synthesized by the fibroblast. Leucocytes, mastocytes or even tissue macrophages are also found therein. It also contains blood vessels and nerve fibres.
The epidermis is a desquamating multilayered epithelium with an average thickness of 100 .mu.m and is conventionally divided into a basal layer of keratinocytes, which constitutes the germinal layer of the epidermis, a so-called prickle cell layer, composed of several layers of polyhedral cells positioned on the germinal cells, a so-called granular layer, composed of flattened cells comprising distinct cytoplasmic inclusions, keratohyalin granules, and finally an upper layer, known as the horny layer (or stratum corneum), composed of keratinocytes at the terminal stage of their differentiation, known as corneocytes. The latter are anucleate mummified cells which derive from keratinocytes. The stacking of these corneocytes constitutes the horny layer which is responsible, inter alia, for the barrier function of the epidermis.
Epidermal differentiation follows a continuous and controlled maturing process in which the basal keratinocytes are converted while migrating, in order to result in the formation of corneocytes, dead cells which are completely keratinized. This differentiation is the consequence of perfectly coordinated phenomena which will result in the maintenance of a constant thickness and thus ensure the homeostasis of the epidermis. This involves regulating the number of cells which take part in the differentiation process and the number of cells which desquamate.
During the normal desquamation process, only the corneocytes closest to the surface detach from the surface of the epidermis.
It is known that, during chronobiological ageing, the thickness of the epidermis is reduced. The cell divisions of the basal layer decrease in number. The renewal time of the horny cells lengthens. The maturing of these cells is incomplete and the keratinization no longer results in the creation of an even and homogeneous horny layer.
It is also known that prolonged and/or repeated exposure to the sun produces fairly similar results on the epidermis. This is photoinduced ageing. It is also known that, in the case of certain diseases, such as ichthyosis, the skin is subjected to damage due to lack of cell proliferation.
It is also known that, at the menopause, cutaneous ageing accelerates, the thickness of the skin decreases and women complain that their skin feels tight and that it takes on the look of a "dry skin", indeed of the appearance of xerosis. It is known that hormonal deficiencies associated with the menopause are accompanied by a general slowing down of the cell metabolism, from which it might all the same be supposed that the effects which women experience are related in particular to a decrease in the proliferation of keratinocytes.
The need to have available a means for facilitating cell multiplication, in particular the multiplication of the cells of the epidermis, is then understood. This is because such means make it possible to facilitate the regeneration of the epidermis and to restore a youthful appearance to the skin.
How such products could be useful in the case of cicatrization is also assessed.